1. Field of the Invention
The present invention relates to a time delay valve disposed in a hydraulic motor to delay the brake time until it is completely braked, and more particularly to a time delay valve disposed incorporated in a casted-housing of the hydraulic motor to be prevented from being damaged.
2. Prior Art
When a hydraulic motor having been rotated is braked abruptly, a shock generated by the abrupt stop of the motor is apt to break parts of the hydraulic motor and shortens the life of the hydraulic motor. To avoid such a shock, it is general that a time delay valve is provided at the hydraulic motor to delay the time for braking-the motor.
Especially in a swing motor which is a hydraulic motor of relatively large size used for a construction equipment, there is a possibility of danger that the interior of the swing motor is seriously damaged when a parking brake used for braking the swing motor is operated abruptly, because the inertial force of the swing motor is large. Therefore, it is essential that the swing motor is provided with a time delay valve so that the parking brake is operated after the swing motor is completely stopped.
Referring to FIG. 1 showing a conventional brake system for a hydraulic motor, a brake piston 103 is elastically supported by a spring 105 at one side of the interior of a hydraulic motor housing 101. In the brake system, first disc plate 107 protruding from the inner wall of housing 101 are engaged with/disengaged from second disc plate 111 protruding from the outer wall of a cylinder block 109 according to the movement of brake piston 103 by an oil pressure applied to piston 103, and accordingly the hydraulic motor is braked/released. In the meantime, as shown in detail in FIG. 2, a time delay valve 131, which is separately manufactured, is assembled at one side of hydraulic motor housing 101 by a plurality of bolts 133, a spring washer 135 is disposed between an outer contact surface of time delay valve 131 and the head of each bolt 133 so as to prevent bolt 133 from being released.
Meanwhile, in the conventional time delay valve having the above described construction, bolts 133 are apt to be damaged because it is exposed to impacts which can be generated in the course of the operation of valve. Such a damage has a bad effect on the entire hydraulic motor, and can cause a severe problem on an entire equipment in which the motor is installed.
Further, there are so many restrictions and inconveniences in installing and moving the hydraulic motor because time delay valve 131 protrudes so far from hydraulic motor housing 101. Furthermore, not only the oil flowing path is complicated and thereby the formation of the path is difficult, but also O-rings for preventing the leakage of oil must be disposed at contact portions between the outer wall of hydraulic motor housing 101 and components such as a spool 137 and an orifice spool 139, so that the manufacturing process of the valve is very complicated and accordingly the manufacturing cost thereof is increased.
Besides, because spring 141 elastically supporting orifice spool 139 must be replaced with a new one to reset or change the delay time, and because the time delay valve must be completely separated from the hydraulic motor housing to replace the spring with a new one, resetting or changing the delay time is very complicated and inconvenient.